20 research outputs found
Toric anti-self-dual Einstein metrics via complex geometry
Using the twistor correspondence, we give a classification of toric
anti-self-dual Einstein metrics: each such metric is essentially determined by
an odd holomorphic function. This explains how the Einstein metrics fit into
the classification of general toric anti-self-dual metrics given in an earlier
paper (math.DG/0602423). The results complement the work of Calderbank-Pedersen
(math.DG/0105263), who describe where the Einstein metrics appear amongst the
Joyce spaces, leading to a different classification. Taking the twistor
transform of our result gives a new proof of their theorem.Comment: v2. Published version. Additional references. 14 page
Toric anti-self-dual 4-manifolds via complex geometry
Using the twistor correspondence, this article gives a one-to-one
correspondence between germs of toric anti-self-dual conformal classes and
certain holomorphic data determined by the induced action on twistor space.
Recovering the metric from the holomorphic data leads to the classical problem
of prescribing the Cech coboundary of 0-cochains on an elliptic curve covered
by two annuli. The classes admitting Kahler representatives are described; each
such class contains a circle of Kahler metrics. This gives new local examples
of scalar-flat Kahler surfaces and generalises work of Joyce who considered the
case where the distribution orthogonal to the torus action is integrable.Comment: 25 pages, 2 figures, v2 corrected some misprints, v3 corrected more
misprints, published version (minus one typo
Off-shell N=2 tensor supermultiplets
A multiplet calculus is presented for an arbitrary number n of N=2 tensor
supermultiplets. For rigid supersymmetry the known couplings are reproduced. In
the superconformal case the target spaces parametrized by the scalar fields are
cones over (3n-1)-dimensional spaces encoded in homogeneous SU(2) invariant
potentials, subject to certain constraints. The coupling to conformal
supergravity enables the derivation of a large class of supergravity
Lagrangians with vector and tensor multiplets and hypermultiplets. Dualizing
the tensor fields into scalars leads to hypermultiplets with hyperkahler or
quaternion-Kahler target spaces with at least n abelian isometries. It is
demonstrated how to use the calculus for the construction of Lagrangians
containing higher-derivative couplings of tensor multiplets. For the
application of the c-map between vector and tensor supermultiplets to
Lagrangians with higher-order derivatives, an off-shell version of this map is
proposed. Various other implications of the results are discussed. As an
example an elegant derivation of the classification of 4-dimensional
quaternion-Kahler manifolds with two commuting isometries is given.Comment: 36 page
A holonomy characterisation of Fefferman spaces
We prove that Fefferman spaces, associated to non--degenerate CR structures
of hypersurface type, are characterised, up to local conformal isometry, by the
existence of a parallel orthogonal complex structure on the standard tractor
bundle. This condition can be equivalently expressed in terms of conformal
holonomy. Extracting from this picture the essential consequences at the level
of tensor bundles yields an improved, conformally invariant analogue of
Sparling's characterisation of Fefferman spaces.Comment: AMSLaTeX, 15 page
On NS5-brane instantons and volume stabilization
We study general aspects of NS5-brane instantons in relation to the
stabilization of the volume modulus in Calabi-Yau compactifications of type II
strings with fluxes, and their orientifold versions. These instantons correct
the Kahler potential and generically yield significant contributions to the
scalar potential at intermediate values of string coupling constant and volume.
Under suitable conditions they yield uplifting terms that allow for
meta--stable de Sitter vacua.Comment: 29 pages, 3 figures; statements about fields G^a made more precise,
added some clarifications, typos correcte
The twistor spinors of generic 2- and 3-distributions
Generic distributions on 5- and 6-manifolds give rise to conformal structures
that were discovered by P. Nurowski resp. R. Bryant. We describe both as
Fefferman-type constructions and show that for orientable distributions one
obtains conformal spin structures. The resulting conformal spin geometries are
then characterized by their conformal holonomy and equivalently by the
existence of a twistor spinor which satisfies a genericity condition. Moreover,
we show that given such a twistor spinor we can decompose a conformal Killing
field of the structure. We obtain explicit formulas relating conformal Killing
fields, almost Einstein structures and twistor spinors.Comment: 26 page
Domain walls of N=2 supergravity in five dimensions from hypermultiplet moduli spaces
We study domain wall solutions in d=5, N=2 supergravity coupled to a single
hypermultiplet whose moduli space is described by certain inhomogeneous, toric
ESD manifolds constructed recently by Calderbank and Singer. Upon gauging a
generic U(1) isometry of these spaces, we obtain an infinite family of models
whose "superpotential" admits an arbitrary number of isolated critical points.
By investigating the associated supersymmetric flows, we prove the existence of
domain walls of Randall-Sundrum type for each member of our family, and find
chains of domain walls interpolating between various AdS_5 backgrounds. Our
models are described by a discrete infinity of smooth and complete
one-hypermultiplet moduli spaces, which live on an open subset of the minimal
resolution of certain cyclic quotient singularities. These spaces generalize
the Pedersen metrics considered recently by Behrndt and Dall' Agata.Comment: 39 pages, numerous figures; v4: two references adde
M-theory on `toric' G_2 cones and its type II reduction
We analyze a class of conical G_2 metrics admitting two commuting isometries,
together with a certain one-parameter family of G_2 deformations which
preserves these symmetries. Upon using recent results of Calderbank and
Pedersen, we write down the explicit G_2 metric for the most general member of
this family and extract the IIA reduction of M-theory on such backgrounds, as
well as its type IIB dual. By studying the asymptotics of type II fields around
the relevant loci, we confirm the interpretation of such backgrounds in terms
of localized IIA 6-branes and delocalized IIB 5-branes. In particular, we find
explicit, general expressions for the string coupling and R-R/NS-NS forms in
the vicinity of these objects. Our solutions contain and generalize the field
configurations relevant for certain models considered in recent work of Acharya
and Witten.Comment: 45 pages, references adde
Intersecting 6-branes from new 7-manifolds with G_2 holonomy
We discuss a new family of metrics of 7-manifolds with G_2 holonomy, which
are R^3 bundles over a quaternionic space. The metrics depend on five
parameters and have two Abelian isometries. Certain singularities of the G_2
manifolds are related to fixed points of these isometries; there are two
combinations of Killing vectors that possess co-dimension four fixed points
which yield upon compactification only intersecting D6-branes if one also
identifies two parameters. Two of the remaining parameters are quantized and we
argue that they are related to the number of D6-branes, which appear in three
stacks. We perform explicitly the reduction to the type IIA model.Comment: 25 pages, 1 figure, Latex, small changes and add refs, version
appeared in JHE
K\"{a}hler-Einstein metrics on strictly pseudoconvex domains
The metrics of S. Y. Cheng and S.-T. Yau are considered on a strictly
pseudoconvex domains in a complex manifold. Such a manifold carries a complete
K\"{a}hler-Einstein metric if and only if its canonical bundle is positive. We
consider the restricted case in which the CR structure on is
normal. In this case M must be a domain in a resolution of the Sasaki cone over
. We give a condition on a normal CR manifold which it cannot
satisfy if it is a CR infinity of a K\"{a}hler-Einstein manifold. We are able
to mostly determine those normal CR 3-manifolds which can be CR infinities.
Many examples are given of K\"{a}hler-Einstein strictly pseudoconvex manifolds
on bundles and resolutions.Comment: 30 pages, 1 figure, couple corrections, improved a couple example